The present invention relates to an exposure apparatus suitable for manufacturing a semiconductor element, image sensing element, liquid crystal display element, thin-film magnetic head, and any other microdevices.
Photolithography for manufacturing a semiconductor element or the like adopts an exposure apparatus which exposes a photosensitive substrate to the pattern image of a mask (e.g., reticle) via a projection optical system. Recently, semiconductor integrated circuits have been developed toward micropatterning, and the wavelength of a photolithography light source is being decreased in photolithography.
Such an exposure apparatus suffers a decrease in the intensity of exposure light under the influence of absorption of exposure light by oxygen in the use of, as exposure light, vacuum ultraviolet rays, particularly, light with a wavelength shorter than 250 nm such as a KrF excimer laser beam (wavelength: 248 nm), an ArF excimer laser beam (wavelength: 193 nm), or an F2 laser beam (wavelength: 157 nm), harmonic light such as a YAG laser beam, or X-rays.
The prior art avoids a decrease in the transmittance of light as follows: a closed space which confines only an optical path is formed in an exposure apparatus having a light source such as an F2 excimer laser, and gas in the closed space is purged with gas such as nitrogen not containing oxygen.
FIG. 32 is a view showing an exposure apparatus which executes exposure by supplying inert gas into a space defined by an optical member on the final stage of a projection optical system (lens barrel) and a photosensitive substrate (wafer) and forming an inert gas atmosphere in the space. In this exposure apparatus, a shielding member is arranged around the space in order to separate the space in the exposure region from an ambient atmosphere. Inert gas is supplied from the vicinity of the exposure region to the space.
The exposure apparatus shown in FIG. 32 requires several sec until the oxygen concentration in the space in the exposure region decreases after a wafer stage is driven to load a wafer into the exposure region. This results in low throughput.
The same problem occurs when inert gas is supplied to the vicinity of a reticle. Also for the reticle, the exposure apparatus requires several sec until the oxygen concentration in a space surrounded by a shielding member decreases, which decreases the throughput.
The present invention has been made in consideration of the above situation, and has as its object to shorten a time required to purge, with inert gas, gas in an optical path space including a space (exposure region) through which exposure light passes, such as a space between a projection optical system and a substrate, a space between an illumination optical system which illuminates a mask (e.g., reticle) and a mask stage which holds the mask, and a space between the mask stage and the projection optical system, and/or to maintain the purity or concentration of inert gas in the optical path space at a proper level.
To achieve the above object, according to the present invention, there is provided an exposure apparatus which projects and transfers a pattern formed on a mask to a substrate by using exposure light, comprising a stage, an optical system, and a gas flow formation mechanism which forms a flow of inert gas in an optical path space including a space through which exposure light passes between the stage and the optical system, wherein the gas flow formation mechanism forms a flow of inert gas having a spatially or temporally nonuniform distribution in the optical path space. This arrangement can shorten a time required to purge gas in an optical path space with inert gas, and/or maintain the purity or concentration of inert gas in the optical path space at a proper level.
According to a preferred aspect of the present invention, the gas flow formation mechanism forms a flow of inert gas having a nonuniform flow velocity distribution in the optical path space, as a flow of inert gas having a spatially nonuniform distribution.
More specifically, it is preferable that the gas flow formation mechanism comprise a supply mechanism which supplies inert gas to the optical path space, and that the supply mechanism supply inert gas having a nonuniform flow velocity distribution to the optical path space.
Alternatively, it is preferable that the gas flow formation mechanism comprise a supply mechanism which supplies inert gas to the optical path space, and an exhaust mechanism which exhausts gas containing inert gas from the optical path space, and that the exhaust mechanism exhaust the gas containing the inert gas from the optical path space so as to form a nonuniform flow velocity distribution in the optical path space.
According to another preferred aspect of the present invention, the nonuniform flow velocity distribution preferably includes a distribution in which a flow velocity is higher at a portion closer to the optical system. The flow of inert gas can be formed in a direction apart from the optical system, and gas in the optical path space can be efficiently exhausted.
Alternatively, according to still another preferred aspect of the present invention, the nonuniform flow velocity distribution preferably includes a distribution in which a flow velocity is higher at a portion closer to an optical axis of the optical system. The flow of inert gas can be formed from the optical path space toward an ambient space, and gas in the optical path space can be efficiently exhausted.
According to still another preferred aspect of the present invention, the supply mechanism preferably comprises two gas supply portions arranged at positions opposite to each other via the optical path space. This can further increase the exhaust efficiency.
As means for forming a flow of inert gas having a temporally nonuniform distribution, e.g., a flow of inert gas whose flow velocity temporally changes, according to still another preferred aspect of the present invention, the gas flow formation mechanism comprises a supply mechanism which supplies inert gas to the optical path space, and the supply mechanism changes a flow rate of inert gas supplied to the optical path space along with a lapse of time. Since gas in the optical path space can be stirred, the purge time can be shortened.
According to still another preferred aspect of the present invention, it is preferable that the gas flow formation mechanism comprise two gas supply portions arranged at positions opposite to each other via the optical path space, and that inert gas be supplied to the optical path space to make a flow of gas in the optical path space nonuniform.
The two gas supply portions preferably supply different supply amounts of inert gas to the optical path space or to change flow rates of inert gas along with a lapse of time. This can enhance the stirring effect.
It is more preferable that the gas flow formation mechanism comprise at least two supply mechanisms which supply inert gas to the optical path space, and that the at least two supply mechanisms be controlled to supply different supply amounts of inert gas from the respective supply mechanisms or to change flow rates of inert gas supplied from the respective supply mechanisms along with a lapse of time. This can further enhance the stirring effect.
The at least two supply mechanisms are controlled to change flow rates of inert gas supplied from the respective supply mechanisms to the optical path space along with a lapse of time while a sum of the flow rates of inert gas supplied from the respective supply mechanisms to the optical path space is kept almost constant. The stirring effect can be enhanced while the consumption amount of inert gas is kept constant.
The gas flow formation mechanism preferably changes a flow of inert gas formed in the optical path space in accordance with a change in positional relationship between the stage and the optical path space. Alternatively, it is preferable that the gas flow formation mechanism comprise a supply mechanism which supplies inert gas to the optical path space, and an exhaust mechanism which exhausts gas containing inert gas from the optical path space, and that the supply mechanism and the exhaust mechanism change a supply amount and an exhaust amount in accordance with a change in positional relationship between the stage and the optical path space. The exhaust (purging) efficiency can be improved while reducing the amount of necessary inert gas.
More specifically, the gas flow formation mechanism preferably evacuates the optical path space by a predetermined exhaust amount when a predetermined region of the stage starts to enter the optical path space, and decreases the exhaust amount after the predetermined region of the stage completely enters the optical path space.
Alternatively, the gas flow formation mechanism preferably evacuates the optical path space by a predetermined exhaust amount when a predetermined region of the stage starts to enter the optical path space, and stops exhaust after the predetermined region of the stage completely enters the optical path space.
Alternatively, it is preferable that the gas flow formation mechanism comprise a supply mechanism which supplies inert gas to the optical path space, and a supply/exhaust mechanism which supplies inert gas to the optical path space or exhausts gas containing inert gas from the optical path space, and that the gas flow formation mechanism cause the supply mechanism to supply inert gas to the optical path space and operate the supply/exhaust mechanism as an exhaust mechanism when a predetermined region of the stage starts to enter the optical path space, and operate the supply/exhaust mechanism as an air supply mechanism after a lapse of predetermined time.
According to still another preferred aspect of the present invention, the gas flow formation mechanism comprises a plurality of flow rate controllers, and a plurality of air supply ports respectively connected to the plurality of flow rate controllers, and the plurality of flow rate controllers form a nonuniform flow velocity distribution.
Alternatively, the gas flow formation mechanism may form a nonuniform flow velocity distribution by the plurality of flow rate controllers using a plurality of filters having different pressure losses.
According to still another preferred aspect of the present invention, the exposure apparatus preferably further comprises a shielding portion which separates at least part of a side plane of the optical path space from an ambient space around the optical path space. This arrangement makes it easy to increase the purge efficiency in the optical path space and maintain the purity or concentration of inert gas in the optical path space at a proper level.
The exposure apparatus preferably further comprises a shielding portion which separates a plane having no gas flow formation mechanism out of side planes of the optical path space from an ambient space around the optical path space.
According to still another preferred aspect of the present invention, the nonuniform flow velocity distribution preferably includes a distribution in which a flow velocity is higher at a periphery apart from an optical axis of the optical system. For example, entrance of an ambient atmosphere from an ambient space to the optical path space can be suppressed upon the completion of purge, and the purity or concentration of inert gas in the optical path space can be maintained at an appropriate level.
According to still another preferred aspect of the present invention, it is preferable that the gas flow formation mechanism comprise a plurality of flow rate controllers, and a plurality of air supply ports respectively connected to the plurality of flow rate controllers, and that the plurality of flow rate controllers form a nonuniform flow velocity distribution.
Alternatively, it is preferable that the gas flow formation mechanism comprise a plurality of air supply ports arranged to supply inert gas in a predetermined direction, and that an outer air supply port out of the plurality of air supply ports project in the predetermined direction.
According to still another preferred aspect of the present invention, it is preferable that the gas flow formation mechanism comprise a supply mechanism which supplies inert gas to the optical path space, and an exhaust mechanism which exhausts gas containing inert gas from the optical path space, and that the exhaust mechanism be arranged at a position opposite to the supply mechanism via the optical path space.
Alternatively, according to still another preferred aspect of the present invention, the gas flow formation mechanism preferably comprises two gas supply portions arranged at positions opposite to each other via the optical path space. In this case, the gas flow formation mechanism preferably comprises two gas exhaust portions arranged at positions opposite to each other via the optical path space.
According to still another preferred aspect of the present invention, the exposure apparatus preferably further comprises a wall arranged at a position opposite to the supply mechanism via a center of the optical path space with a surface of the wall facing to the center.
According to still another preferred aspect of the present invention, the exposure apparatus preferably further comprises a shielding portion which separates at least part of a side plane of the optical path space from an ambient space around the optical path space. This arrangement can further suppress entrance of an ambient atmosphere from an ambient space to the optical path space. The exposure apparatus preferably further comprises a shielding portion which separates a plane having no gas flow formation mechanism out of side planes of the optical path space from an ambient space around the optical path space. The shielding portion may be formed by a flow of inert gas.
According to still another preferred aspect of the present invention, the gas flow formation mechanism preferably supplies inert gas to the optical path space so as to adjust the optical path space to a positive pressure with respect to an ambient space.
According to still another preferred aspect of the present invention, at least part of the shielding portion is preferably formed from a member which transmits alignment light.
According to still another preferred aspect of the present invention, the exposure apparatus preferably further comprises a substrate stage, a substrate chuck mounted on the substrate stage, and a member which smooths a change in level between a substrate chucked by the substrate chuck and an ambient portion.
According to still another preferred aspect of the present invention, the shielding portion which defines the optical path space preferably changes a length to the photosensitive substrate, thereby increasing the exhaust efficiency in the optical path space.
According to still another preferred aspect of the present invention, the gas flow formation mechanism is arranged to form a flow of inert gas in, e.g., an optical path space between a projection optical system and the substrate.
According to still another preferred aspect of the present invention, the gas flow formation mechanism is arranged to form a flow of inert gas in, e.g., an optical path space between an illumination system which illuminates the mask and a mask stage which holds the mask.
According to still another preferred aspect of the present invention, the gas flow formation mechanism is arranged to form a flow of inert gas in, e.g., an optical path space between a mask stage which holds the mask and a projection optical system.
According to still another preferred aspect of the present invention, the gas flow formation mechanism preferably comprises a first gas flow formation mechanism arranged to form a flow of inert gas in a first optical path space between a projection optical system and the substrate, a second gas flow formation mechanism arranged to form a flow of inert gas in a second optical path space between an illumination system which illuminates the mask and a mask stage which holds the mask, and a third gas flow formation mechanism arranged to form a flow of inert gas in a third optical path space between the mask stage and the projection optical system.
According to still another preferred aspect of the present invention, the inert gas includes nitrogen gas or helium gas.
A device manufacturing method according to the present invention comprises the steps of transferring a pattern to a substrate coated with a photosensitive material by using the above-described exposure apparatus, and developing the substrate.
Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof.